1. Field of the Invention
The instant invention relates to a process for removing a species from a fluid which comprises (a) contacting said fluid with a hollow microcapsule, said microcapsule having a wall surrounding an internal void, said wall being substantially insoluble in said fluid and said species being permeable to said wall; (b) permeating said species through said wall into said void; (c) converting said permeated species, in said void into a species which is impermeable to said wall; (d) separating said microcapsule from said fluid; (e) converting the impermeable species of step (c) into a species which is permeable to said wall; and (f) permeating the permeable species of step (e) through said wall. Preferably said void contains a reagent which together with said permeated species form a reversible oxidation-reduction couple. In the instant preferred embodiment said permeated species is converted into an impermeable species by means of said oxidation-reduction reaction to trap said impermeable species in said void. The spent microcapsules, i.e. microcapsules are no longer capable of converting the permeable species of step (c) into an impermeable species, are regenerated by reconverting the impermeable species into a permeable species by reversing such oxidation-reduction reaction by means of heat, light, or the absence of light. The instant process is particularly preferred for separating multivalent metal ions from aqueous solutions.
2. Description of the Prior Art
Encapsulation or micro-encapsulation is generally considered as a special form of packaging wherein individual particles which can be liquid, gaseous, or solid in nature are individually coated for protection against the environment. Such microcapsules are utilized in adhesives, agricultural chemicals, food products, graphic arts, household cleansers and detergents, paints and sealants, pharmaceuticals, fuels, rubber chemicals, paper and paper products, cosmetics, and magnetics. In none of the above industries are microcapsules utilized as a separation means and it is apparent why this is so. Microcapsules, in general, are utilized on a one-time basis, that is, when material which is encapsulated is to be released, the capsules are either broken for an abrupt release or the material contained in the capsules is slowly released into the environment by permeation through the capsule wall. Heretofore, no one, has commercially utilized microcapsules as a separation medium. Moreover, no one has regenerated active microcapsules, after use as a separation medium, by permeating the separated material out of the capsule and recovering the microcapsules for reuse.